Williams was affectionate throughout the night, touching the back of Segel's head, running her fingers through his hair and gently brushing his hair around his ear. They flirted and laughed together while sipping wine – white for him, red for her.

Williams would often wrap her arm around Segel and hug him. At one point, he made a funny comment, and she grabbed him by the shoulders and made him fall on top of her. They left in separate SUVs after an hour of socializing.

Like Segel's new film, Williams's is about commitment and marriage. In it, the three-time Oscar nominee plays a young wife who is tempted by another man.

"I feel like every project grows me up and changes me," she told PEOPLE on the red carpet. "I hadn't quite hit 30 when I made this movie, and to me that's a big part of what this film is about, making that transition and leaving your girlhood behind and becoming a woman."

Asked about her character's troubles, she replied: "There's many hard parts of relationships. I think that's what the movie's about, but I don't know because I've never been married. I don't really know what those first few years [of marriage] are like, but I hope they're great."